Welcome to Your AS 2 Practical Investigation Guide
Hello and welcome! In Unit AS 2 (Internal Assessment – Renewable Energy Technologies), you get to step into the shoes of a real-world renewable energy engineer. This unit makes up 50% of your AS Level (and 20% of your total A Level).
Instead of sitting a written exam for this unit, you will complete an independent technical report. You will investigate a realistic client scenario (such as a farm, a community building, a business, or a home), conduct hands-on laboratory experiments, analyze real technical data, and present a professional recommendation.
Don't worry if this sounds like a lot of work right now! We are going to break down the entire practical investigation step-by-step so that you understand exactly what to do, what formulae to use, and how to achieve top marks.
Stage 1: Understanding the Scenario and Context
Every engineering project begins with a client problem. In AS 2, your investigation is framed around a specific site context, such as:
• Domestic Site: A family home wanting to reduce grid electricity bills or switch from fossil fuel heating.
• Agricultural / Farm Site: A farm with high thermal demands (e.g., dairy washing or grain drying) and large land/roof areas.
• Commercial / Business Site: An office or warehouse looking to reduce its carbon footprint and operational costs.
• Community Site: A local sports hall or school aiming for energy self-sufficiency.
Why does context matter? You cannot simply choose a technology because you like it. Your practical work must directly answer the client's unique needs, physical layout, and geographical conditions.
Stage 2: Desktop Research and Literature Review
Before touching any laboratory equipment, you must carry out secondary research. This means researching the fundamental science, operating principles, advantages, and limitations of the core renewable energy technologies:
• Wind Energy: Horizontal and vertical axis turbines, wind velocity profiles, and siting requirements.
• Solar Photovoltaic (PV): Converting sunlight directly into electrical energy using semiconductor materials.
• Solar Thermal: Absorbing solar radiation to heat water or transfer fluids directly.
• Biomass: Generating heat through the combustion of organic fuels (such as wood pellets, logs, or agricultural residues).
Top Tip: Keep track of every website, book, or technical datasheet you consult. You must cite these using standard Harvard referencing in your final report bibliography.
Stage 3: Designing and Setting Up Your Practical Investigation
The heart of AS 2 is your empirical (hands-on) laboratory investigation. You will test a renewable technology rig to gather primary data.
1. Formulating an Aim and Hypothesis
• Aim: A clear statement of what you intend to measure (e.g., "To investigate how varying the angle of incidence affects the electrical power output and efficiency of a monocrystalline solar PV panel.")
• Hypothesis: A scientific prediction with a reasoned explanation (e.g., "As the angle of incidence approaches \(90^\circ\) perpendicular to the light source, the electrical power output will reach its maximum because the solar irradiance intercepted per unit area is at its highest.")
2. Identifying Experimental Variables
• Independent Variable (IV): The factor you deliberately change (e.g., blade pitch angle, wind speed, tilt angle of a solar panel, or fuel mass burned).
• Dependent Variable (DV): The factor you measure as an outcome (e.g., voltage and current generated, water temperature increase, or electrical power output).
• Controlled Variables (CV): Factors you must keep strictly constant to ensure a fair test (e.g., distance between the lamp and solar panel, ambient room temperature, or water volume).
3. Rigorous Health and Safety Risk Assessment
Engineering work requires strict adherence to UK health and safety protocols. You must produce a dedicated risk assessment table before carrying out laboratory experiments. Examiners look for specific, realistic hazards rather than generic statements:
• Rotating Turbine Blades: Risk of physical impact or entanglement. Control Measure: Install safety guards or maintain a clear exclusion zone while the turbine is spinning.
• High-Intensity Lamps / Solar Simulators: Risk of thermal burns or eye strain. Control Measure: Allow equipment to cool before handling; do not stare directly into halogen light sources.
• Biomass Combustion / Calorimetry: Risk of open flames, hot water scalds, and particulate inhalation. Control Measure: Carry out burning in a well-ventilated space or fume cupboard; wear heat-resistant gloves and safety goggles; have a fire blanket immediately accessible.
• Electrical Circuits: Risk of short circuits or electric shock. Control Measure: Inspect all leads and connections before switching on power supplies; keep liquids away from multimeters and wiring.
Key Takeaway for Stage 3: A great scientific investigation always has one clear independent variable, tightly controlled parameters, and a thorough, safety-first risk assessment.
Stage 4: Essential Formulae and Data Analysis
Once you have collected your laboratory data in well-structured tables using proper SI units, you must process the results using standard engineering formulae. Let's look at the core calculations for each technology.
A. Wind Turbine Calculations
The kinetic power available in moving air depends heavily on wind velocity.
Kinetic Power in the Wind Formula:
\(P_{\text{wind}} = \frac{1}{2} \rho A v^3\)
Where:
• \(P_{\text{wind}}\) = Total power available in the wind (Watts, \(\text{W}\))
• \(\rho\) (rho) = Air density (typically \(1.225 \text{ kg/m}^3\) at standard sea-level temperature and pressure)
• \(A\) = Swept area of the rotor blades (\(\text{m}^2\)), calculated as \(A = \pi r^2\) (where \(r\) is the blade radius in metres)
• \(v\) = Wind velocity in metres per second (\(\text{m/s}\))
Crucial Concept — The Betz Limit: No wind turbine can ever convert \(100\%\) of the wind's kinetic energy into mechanical power, because the air must keep moving away from the blades. The theoretical maximum aerodynamic efficiency is the Betz Limit, which is \(\frac{16}{27} \approx 59.3\%\).
B. Solar Photovoltaic (PV) Calculations
To find out how effectively a solar panel converts light energy into electricity, follow these two steps:
Step 1: Calculate Electrical Power Output (\(P_{\text{el}}\))
\(P_{\text{el}} = V \times I\)
Where:
• \(V\) = Voltage measured across the load (Volts, \(\text{V}\))
• \(I\) = Current flowing through the circuit (Amperes, \(\text{A}\))
• \(P_{\text{el}}\) = Electrical power output (Watts, \(\text{W}\))
Step 2: Calculate Solar PV Conversion Efficiency (\(\eta\))
\(\eta = \frac{P_{\text{out}}}{P_{\text{in}}} \times 100\% = \frac{V \times I}{G \times A} \times 100\%\)
Where:
• \(G\) = Solar irradiance hitting the panel (\(\text{W/m}^2\))
• \(A\) = Surface area of the photovoltaic panel module (\(\text{m}^2\))
• \(\eta\) = System efficiency percentage (\(\%\))
C. Solar Thermal and Biomass Energy Calculations
When testing solar thermal collectors or burning biomass fuel in a calorimeter, you measure the heat energy transferred to a known volume of water.
Heat Energy Transferred Formula:
\(Q = mc\Delta T\) (or \(E = mc\Delta T\))
Where:
• \(Q\) or \(E\) = Thermal energy absorbed by the fluid (Joules, \(\text{J}\))
• \(m\) = Mass of the fluid being heated (\(\text{kg}\)) — Note: \(1 \text{ litre of water} = 1 \text{ kg}\)
• \(c\) = Specific heat capacity of water (\(\approx 4182 \text{ J/kg}^\circ\text{C}\))
• \(\Delta T\) = Temperature rise (\(T_{\text{final}} - T_{\text{initial}}\) in \(^\circ\text{C}\))
Biomass Specific Energy / Energy Density:
\(\text{Specific Energy} = \frac{E}{\Delta m_{\text{fuel}}}\)
Where \(\Delta m_{\text{fuel}}\) is the mass of biomass consumed during combustion (giving energy density in \(\text{J/g}\) or \(\text{MJ/kg}\)).
Stage 5: Synthesis, Recommendations, and Evaluation
This final stage is where you earn high-level marks by bridging your laboratory findings with the real-world client scenario.
1. Linking Lab Data to Real Site Constraints
Do not simply state: "Solar PV was \(15\%\) efficient in the lab, so the client should buy solar panels." Instead, evaluate real-world feasibility:
• Resource Availability: Does the client site receive adequate annual solar irradiance or average wind speeds (\(\text{m/s}\))?
• Physical Site Constraints: Roof orientation (e.g., South-facing in the UK), roof pitch/tilt angle, structural loading capacity, and shading from nearby trees or structures.
• Financial Feasibility: Capital installation cost versus estimated annual savings and financial payback period.
• Environmental Impact: Estimated carbon dioxide (\(\text{CO}_2\)) emission reductions compared to grid electricity or fossil heating.
2. Critical Evaluation of Practical Work
Reflect honestly on your experimental method:
• Were there experimental errors (e.g., heat losses to the room during calorimetry, parallax error when reading analogue meters, or fluctuating fan speeds)?
• How could the reliability and validity of the experiment be improved if repeated?
How Your AS 2 Report is Marked
Your technical report is marked internally by your teacher and externally moderated by CCEA across three Assessment Objectives:
• AO1 (Knowledge and Understanding): Clear explanation of renewable technologies, scientific concepts, and technical terminology.
• AO2 (Application of Knowledge and Skills): Designing and conducting the investigation, carrying out correct mathematical calculations, and presenting graphs with proper labels, scales, and SI units.
• AO3 (Analysis and Evaluation): Analyzing experimental trends, critically evaluating limitations, and making realistic, evidence-based recommendations tailored to the client scenario.
Standard Technical Report Structure
Ensure your coursework is organized into a formal engineering report structure:
1. Title Page & Contents Page
2. Introduction & Executive Summary (Client brief and project scope)
3. Desktop Research (Literature review of candidate technologies)
4. Methodology & Health and Safety (Hypothesis, apparatus, procedure, and risk assessment)
5. Results & Graphical Analysis (Raw data tables, processed results, graphs, and sample calculations)
6. Discussion & Synthesis (Interpreting trends and applying findings to the client's site)
7. Final Recommendations (System sizing, cost, carbon savings, and site feasibility)
8. Evaluation & Bibliography (Limitations, improvements, and Harvard-style references)
Common Pitfalls to Avoid
Examiner reports frequently highlight the following easy-to-fix mistakes:
• The "Disconnected Practical": Performing a generic bench test without explaining how the numbers help your client make an investment decision.
• Confusing Power and Energy: Power is the rate of energy transfer measured in Watts (\(\text{W}\) or \(\text{kW}\)), whereas Energy is the total work done over time measured in Joules (\(\text{J}\)) or Kilowatt-hours (\(\text{kWh}\)).
• Incorrect SI Units: Forgetting to convert wind speeds from \(\text{km/h}\) to \(\text{m/s}\), or forgetting to convert panel dimensions from \(\text{mm}^2\) to \(\text{m}^2\). Always double-check your units before calculating!
• Ignoring Site Realities: Recommending a large wind turbine in a heavily sheltered urban area or a solar thermal array on a heavily shaded North-facing roof.
Quick Revision Summary
• Unit AS 2 requires a technical report combining desktop research, practical laboratory testing, and a real-world client recommendation.
• Wind Power scales with the cube of velocity: \(P_{\text{wind}} = \frac{1}{2} \rho A v^3\), capped by the Betz limit (\(59.3\%\)).
• Solar PV Efficiency relates electrical power output (\(V \times I\)) to the solar energy input (\(G \times A\)).
• Thermal Energy absorbed by water in solar thermal or biomass calorimetry is calculated via \(Q = mc\Delta T\).
• Top Grades require linking empirical lab data directly to site conditions, payback, and carbon savings while thoroughly evaluating experimental limitations.